World Building: Where to Begin

Start Small

You probably have grand ideas in your head about what your campaign world will be like: cities floating in the clouds, fierce battles, golden plains of wheat stretching to the horizon, things like that. That's good but thinking about such things before pencil hits paper is just going to give you too much to worry about too soon.

Focus on just a single location where your first few play sessions will take place. The GM guides are a great resource for setting up a single coherent location. I recommend this location be a settlement with a nearby adventure. This kind of "starting town with a haunted mine" seems cliche but there's a simple reason it turns up everywhere: It's easy for both the GM and the players. Everyone knows what to expect which means you can focus on getting used to your players and new players can get used to the game. The guidebooks will help you handle the mechanics of a town and the first adventure site, but the look and feel of the place is still up to you.

A Basic, Believable Settlement

...Just add water. Seriously, assuming your setting is using the pseudo-medieval background expected by most game systems then access to water is an essential first step in creating a town. A river or lake provides drinking water, irrigation for crops, a way to move goods, and a source of food.

...Heat/chill until ready. The next consideration is climate. Human civilization springs up in virtually every place with sunlight and access to fresh water, so this is mostly just a flavour decision. Choose carefully though, because no climate exists in a vacuum and when it comes time to zoom the map out and create surrounding areas it will be your job to make the terrain believable.

...Season to taste. Now that you know the climate of your settlement you can actually create the place. I highly recommend basing your settlement on real-world examples from similar climates. Earth has examples of people living in virtually every environment imaginable and reading about places like yours will help you get a clear mental picture of what the place looks like. Once you have that picture in your head you can shape it to fit what you have designed on the mechanical side (races, population, etc) and use that image to describe it at the table.

Conservation of Detail

Now that you have your anchor town as a dot on the map, it's going to be very lonely without some more dots. Good storytelling makes the world seem bigger than just what's on the page. Consider some of the dialogue from the first act of Star Wars: A New Hope. On Tattooine the characters throw out location names like "Anchorhead", "Toshi Station" and "Mos Eisely" in casual conversation, but only one of those places is ever visited in the main storyline. It's good to have such places just for some NPC to say they're from there, have news arrive about there, or just give the players new places to think about once they're settled in your starting village. Just don't get carried away.

Conservation of Detail is about making the areas near the players feel alive and populated without having to design everything up-front. Travel in medieval settings is usually very slow. Few people ever travel beyond the borders of their own county much less to the next nation. What this means for you is that only the area within a few miles of your settlement and adventure site needs to be fleshed out. If there are mountains in the distance, draw them, and if you want a well-known major city in the same region as the players you should know which road leads there but not necessarily where it is.

That's all that's needed to start a new campaign setting. If your players like it there will be more work to finish when they leave the first settlement & adventure site.